In recent years, a photolithographic process used to produce semiconductor devices has been desired to form a finer pattern along with miniaturization of semiconductor devices. Various methods for forming a fine pattern using a photoresist material that responds to short-wavelength light such as KrF excimer laser light, ArF excimer laser light, or F2 excimer laser light have been studied, and a novel photoresist material that responds to short-wavelength light such as excimer laser light has been desired.
Various phenol resin-based photoresist materials have been developed. However, since these materials absorb light to a large extent due to the aromatic ring, it is difficult to obtain pattern accuracy that can deal with miniaturization
In order to deal with the above problem, a polymer obtained by copolymerizing polymerizable compounds having an alicyclic skeleton (e.g., 2-methyl-2-adamantyl methacrylate) has been proposed as a photoresist used for a semiconductor production process that utilizes ArF excimer laser light (see Patent Document 1, for example).
A line width of 32 nm or less is being implemented through the development of microfabrication technology. However, it is difficult to meet various requirements (e.g., adhesion to substrate, exposure sensitivity, resolution, pattern shape, exposure depth, and surface roughness) using only the existing technology. Specifically, the surface of the resulting pattern may show roughness (LER or LWR) or poor flatness when using the existing technology. When using liquid immersion lithography that has been developed in recent years, defects or the like may occur in the resist pattern due to the immersion medium. Moreover, development of a photoresist that exhibits higher sensitivity has been desired for a semiconductor production process that utilizes extreme ultraviolet (EUV) light (wavelength: 13.5 nm) in order to improve the throughput.
A polymer obtained by copolymerizing polymerizable compounds having a cyclic lactone structure has been used as a photoresist used for a semiconductor production process that utilizes ArF excimer laser light in order to improve adhesion to a substrate. 1-(5-Oxo-4-oxa-5-homoadamantyl)methacrylate has been proposed as a lactone having a homoadamantane skeleton, and a photosensitive composition and a pattern-forming method that can form a resist pattern that exhibits high transparency to short-wavelength light and high dry etching resistance, can be developed using an alkali, and exhibits excellent adhesion and resolution have been proposed (see Patent Document 2, for example). However, since a polymerizable compound having a cyclic lactone structure such as the above homoadamantyl methacrylate compound does not have acid-labile properties, such a polymerizable compound does not function as a positive photoresist when used alone. Therefore, it is necessary to copolymerize such a polymerizable compound with an acid-labile monomer such as tert-butyl methacrylate or 2-methyl-2-adamantyl methacrylate.
A photoacid generator (PAG) is indispensable for a positive photoresist in order to implement photosensitivity (dissociation due to acid). Attempts have been made to provide a PAG with acid-labile properties in order to suppress or reduce roughness (LER or LWR) of the surface of the pattern that may occur due to miniaturization (see Patent Documents 3 to 6, for example). However, it is necessary to increase the mutual solubility of a PAG with a photoresist resin, or more uniformly disperse a PAG in a photoresist resin in order to further reduce roughness.
In recent years, an acid-labile unit having an adamantane skeleton or a cyclic lactone structure has been extensively introduced in the development of a low-molecular-weight (monomolecular) positive photoresist that aims at reducing roughness (see Patent Documents 7 to 10, for example). However, satisfactory results have not been obtained by such a method.